This application claims the priority of German patent document 10 2007 050 034.5-35, filed Oct. 17, 2007, the disclosure of which is expressly incorporated by reference herein.
The invention relates to a method and apparatus for monitoring the integrity of satellite navigation signals.
Global Navigation Satellite Systems (GNSS) are used for position indication and navigation on the ground, on water and in the air. GNSS Systems, as, for example, the European Navigation Satellite System currently being constructed (also referred to herein as the Galileo System or simply “Galileo”) include a plurality of satellites, an earth-fixed receiving device system connected with a central computing station, and utilization systems which evaluate and use the satellite signals transmitted by radio by the satellites particularly for navigation.
In a GNSS, a precise detection of a user's position requires local as well as global integrity. “Integrity” in this sense means in particular that, on the one hand, the GNSS is capable of warning a user within a certain time period when parts of the GNSS should not be used for navigation (for example, in the event of a failure of system components), and that on the other hand the user can trust the navigation data which he receives by way of satellite navigation signals from the satellites of the GNSS; that is, he can rely on the precision of the received navigation data.
Known integrity concepts are that of Galileo, of the Wide Area Augmentation System (WAAS) and of the European Geostationary Navigation Overlay Service (EGNOS). In the case of the integrity concept of Galileo, in particular, observations are received only for judging the integrity of a satellite navigation signal when leaving the phase center of the satellite transmission antenna. All other error sources are covered with respect to the integrity by global models, which are necessarily very conservative in order to receive satellite navigation signals that are as reliable or have as much integrity as possible. However, specifically because of this conservative manner of the global models, the efficiency of the integrity system of a GNSS, such as Galileo, is significantly determined by the efficiency of these global models and, in particular, is restricted.
It is therefore an object of the present invention to provide an improved method and apparatus for monitoring the integrity of satellite navigation signals.
This and other objects and advantages are achieved by the method and apparatus for monitoring the integrity of satellite navigation signals, which uses a combination of different detection mechanisms for integrity problems to offer improved integrity services on the one hand, and to improve the efficiency of a GNSS, on the other hand. According to the invention, integrity problems which had already been detected by a detection mechanism, can be taken into account in computing the efficiency of a subsequently implemented detection mechanism for integrity problems of a lower probability. This makes it possible to reduce the demand on the subsequently implemented detection mechanism, and to maintain or improve the efficiency of a GNSS. As an alternative, the efficiency of the subsequently implemented detection mechanism may remain the same and may be offered with a higher-quality, particularly more precise integrity service, because of the combined detection mechanisms. On the whole, the invention permits a better integrity monitoring than can be achieved by means of the known integrity concepts described above.
According to an embodiment of the invention, a method is provided for monitoring the integrity of satellite navigation signals and detecting integrity problems, which has the following steps:
In a first detection of integrity problems the same entity of a navigation signal (that is, the same element or portion of the signal) is received from a certain satellite at different sites, and the received entities are evaluated to estimate and characterize the errors in the signal (and optionally the error in the error determination itself) in order to then finally use this information together with other information to determine the integrity risk.
In a second detection, one or more measurements of one or more received navigation signals from a certain satellite are made and evaluated in order to estimate and characterize the errors in the signals (and optionally the error in the case of the error determination). This information is then used, together with other information, to determine integrity risk. This step is carried out for all signals participating in the position solution.
In a third detection, several navigation signals from different satellites are measured, and the measurements are evaluated to determine the integrity risk. Integrity problems which are detectable during the first and second detection are taken into account only with the probability that they occur during the third detection, and had not been discovered during the first and second detection.
The first and the second detections do not necessarily have to follow one another but can also be carried out in reverse order, or a step can also be omitted completely.
According to an embodiment of the invention, the first detection of integrity problems can always be carried out when an entity of a navigation signal from a certain satellite is received by different observation stations of a satellite navigation system. In this case, it can be ensured that always the same navigation signal entity is processed by the first detection mechanism. A modeling of the error action, as required, for example, in the current Galileo concept (because at a point in time all signals to satellites are measured at an observation station in the case of Galileo so that different observation stations measure different signal entities), can thereby be eliminated in the case of this embodiment of the invention.
According to a further embodiment of the invention, the second detection can comprise a processing at the signal level of the at least one measurement in a receiver for satellite navigation signals. Particularly as a result of a skillful processing at the signal level of one or more signals of a certain satellite, errors can be efficiently detected by means of the second detection mechanism.
Another embodiment of the invention comprises an arrangement for monitoring the integrity of satellite navigation signals which comprises the following:
First detection devices for the first detection of integrity problems, the first detection devices being constructed to receive the same entity of a navigation signal from a certain satellite at different sites and to evaluate the received entities in order to provide information which finally can be used to determine the integrity risk;
second detection devices for the second detection of integrity problems, the second detection devices being constructed to carry out one or more measurements of one or more received navigation signals from a certain satellite and to evaluate the at least one measurement in order to provide information which can finally be used to determine the integrity risk; and
third detection devices for the third detection of integrity problems, the third detection devices being constructed for carrying out measurements of several navigation signals of different satellites and for evaluating the measurements for determining the integrity risk. The third detection devices are also constructed such that integrity problems which can already be detected during the first and second detection are taken into account only with the probability that they occur during the third detection and had not been discovered during the first and second detection. By means of such an arrangement, integrity monitoring can be improved in the case of a satellite navigation system.
According to an embodiment of the invention, the first detection devices can be implemented in different observation stations for satellite navigation signals. For example, the observation stations of an earth-fixed receiving system for satellite navigation signals may comprise the first detection devices. In particular, the first detection devices can be implemented at least partially as a computer program.
Furthermore, according to an embodiment of the invention, each observation station may be constructed such that, when it receives the same entity of the navigation signal from the certain satellite, it evaluates the entity and transmits it to a processing center. As explained above, in this manner it can be ensured that always the same navigation signal entity is evaluated. The evaluation may also not take place before the processing center is reached. The processing center is provided particularly for the processing of signals of the individual observation stations, and for coordinated control of a satellite navigation system. For example, the processing center can be used to generate and distribute integrity warnings in the satellite navigation system.
According to another embodiment of the invention, the second detection devices can be implemented in a receiver for the satellite navigation signals, particularly a processing center for satellite navigation signals or, alternatively, in each user receiver.
Furthermore, according to an embodiment of the invention, the second detection devices can be constructed to carry out the evaluation of the at least one measurement of the received navigation signal from the certain satellite by processing at the signal level.
According to another embodiment of the invention, the third detection devices can be implemented in a receiver for the satellite navigation signals, particularly a processing center for satellite navigation signals or, alternatively, in the user receiver.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.